Heterotopic ossification (HO), the formation of ectopic bone in skeletal muscle and other connective tissues, is an important cause of morbidity from joint immobility and pain. Fibrodysplasia Ossificans Progressiva (FOP), a rare form of HO, is inherited as an autosomal dominant trait and is typically associated with activating mutations in Acvr1, the gene encoding the BMP type I receptor, ALK2. Individuals with FOP only have minimal skeletal abnormalities at birth, but extensive HO affecting nearly all skeletal muscles, ligaments and fascia is triggered after birth by traumatic injury or inflammation. No effective treatments currently exist for FOP patients, and disease progression results in severe restriction of joint function and premature mortality. In 2008, the principal collaborators identified the first small molecule inhibitor of BMP signaling. The compound, dorsomorphin, blocks BMP signaling by inhibiting BMP type I receptors. Dorsomorphin derivatives were developed through initial medicinal chemistry optimization. The overall objective of this research is to advance the development of a dorsomorphin derivative in preparation for clinical testing in patients with FOP. The TRND researchers determined that the initial lead molecule was unsuitable for further preclinical development. As such, TRND scientists performed medicinal chemistry optimization, synthesizing and evaluating with the collaborator over 1000 compounds in vitro. This led to the identification of a compound suitable for formal preclinical development, as well as an additional compound as a back-up. Activities in the lead optimization and development candidate selection included measuring compound efficacy against BMP signaling, assessing specificity and drug-like properties in vitro, and evaluating efficacy and tolerability in vivo.